1. Field of the Invention
This invention relates to a method and system for waste containment and environmental applications, and more particularly, to a cap or liner system constructed of a modified asphalt mixture for use in a waste and environmental containment system.
2. Description of the Related Art
When municipal solid waste and waste and hazardous waste landfills reach their capacities, the waste sites are capped with a final cover that keeps out rainfall and prevents leachate generation and possible environmental contamination. These final covers have traditionally been constructed of layers of clay, sand, vegetated topsoil and, sometimes, geosynthetic materials. Additional sites that require cover include brownfields, spills and industrial sites.
The U.S. Environmental Protection Agency (EPA) has strict regulations for these waste containment and environmental cleanup sites. The EPA has developed a standard of containment that not only includes installations requirements, but also maintenance, monitoring and longevity. Further considerations of the waste site include the cost of installing and maintaining a system, future ability to reuse the site and ongoing inspection considerations.
Most landfill covers in the U.S. are required to meet the minimum regulatory performance standards set forth under the EPA'S Resource Conservation and Recovery Act (RCRA) in subtitles D for municipal landfills (soil cover) and C for hazardous waste landfills (compacted clay cover). Although subtitles D and C do not detail specific cover designs, the regulations allow the governing regulatory agency to consider and approve an alternative final cover as long as it meets the performance standards.
However, most landfills in the U.S. do implement the soil covers and compacted clay cover designs of subtitles D and C, often with little regard for regional conditions. These designs are used even though the EPA has found that a barrier layer composed of clay and a geomembrane under subtitle C is “not very effective” in arid regions. The reason clay barriers were not recommended was because the soil is compacted with more moisture than is needed to achieve optimum density. As the soil dries, it experiences a high level of volume reduction, which leads to cracking caused by shrinkage. The EPA guidelines state: “this traditional cover not only is inherently problematic, but is also very expensive and difficult to construct. Furthermore, the basic soil cover used with Subtitle D also has its problems, as the barrier layer is subject to deterioration due to freeze/thaw cycles.”
Current cover containment practice centers around the use of composite barriers comprised of geomembranes, geosynthetic clay liners (GCL), compacted clay, or amended site soils. Most conventional containment systems are multi-layer geosynthetic or membrane type systems. Installations of these systems are costly due to the multi-layer design. Typically the layers added 2 to 9 feet or more of a cap onto the existing waste or environmental site. These systems were historically subject to damage during construction from equipment, and thereafter from vegetation roots and small animals. Further limitations of the multi-layer membrane systems included difficulty visually inspecting the buried membrane. Rupture of the membrane during installation or thereafter would render the system useless for its intended purpose. Not only was detection of a leak difficult, but repair required excavation of the various layers and risked further damage upon re-exposing the membrane layers. Often due to the nature of the membranes, the site was no longer available for future use as a storage facility or other use due to restrictions on loading.
Other construction materials were historically not sufficiently impermeable or resilient to be used in place of the geosynthetic or membrane. For example, conventional asphalt pavement has a permeability coefficient in the range of 1×10−5 cm/sec with 6–8% air voids. Further, conventional asphalt is typically sensitive to temperature changes. Temperature/Viscosity curves illustrate that conventional asphalt is a liquid at 300° F. when it is mixed, but at very low temperatures can be as brittle as glass.
A 1988 study by the EPA of randomly selected landfills revealed that the vast majority are leaking, and many have caused severe contamination of the groundwater and surrounding ecosystems.
Thus, a waste containment system that meets or exceeds EPA containment requirements, including permeability, longevity, and resilience; allows rapid installation; is easy to maintain; cost effective and provides additional uses for the site once containment is complete, is needed.